Various types of systems are called upon to signal an alarm condition when a specified event occurs. Examples of such systems are fire alarms and burglar alarms. Because of the reliance placed on such systems, steps must be taken to insure the reliability of the alarm circuit. One step which is commonly taken is the use of separate supervisory and alarm modes. In supervisory mode the alarm circuit is monitored to insure that it is in working order, i.e. has no broken wires or other open circuits. When an alarm condition occurs, the circuit shifts from supervisory to alarm mode, causing the alarm to be signaled.
Such alarm circuits may be divided into two general groups. These are known as "class A" circuits and "class B" circuits. A class A circuit has certain fail-safe features not present in a class B circuit. If an open circuit condition occurs in a class B circuit the alarm will not function until the open circuit is repaired. In a class A circuit, however, an open circuit, while detectable by the supervisory mode of the system, will not prevent the alarm from sounding should an alarm condition occur. Class A circuits, therefore, have significant advantages over class B circuits in providing increased safety, by insuring that alarms will be sounded if an alarm condition arises before an open circuit can be repaired.
Alarm systems commonly are designed with a central panel which acts as a controller and various remote sensors and alarms. The design of the central panel will determine whether a class A or a class B alarm circuit may be connected thereto. In some situations, however, it may be desirable to upgrade a system which has been previously installed with class B alarm circuits to class A alarm circuits. Therefore, a system for converting class B alarm circuits to class A is desirable.